Most tractors have an hydraulic system that supplies selective control valves or remotes at the back of the tractor. The hydraulic system also supplies other functions such as steering, brakes, transmission, shift clutches and the point hitches.
For many years nearly all tractors employed open center hydraulics. In open center hydraulic systems, the system's control valves are always open to the reservoir when in the neutral position. As a result, the pump constantly sends oil through the valves and back to the reservoir supplying the pump. These systems are generally preferred for intermittent use. One drawback is that the gear pumps used in these systems are speed sensitive. The faster the engine is run, the higher the flow rate. Also, in these systems heat build up is a problem. Open center systems generate heat from the friction of the constantly flowing oil.
Another type of tractor hydraulic system employs a variable displacement piston pump. These hydraulic systems are called closed center systems. In the closed center system the control valves remain closed to the reservoir and stop fluid flow to the valve while in the neutral position.
This invention relates to an improved hydraulic system primarily for open center hydraulic systems. This system has the benefit of reducing heat and increasing the longevity of a machine. A hydraulic system is a closed system that contains a hydraulic fluid such as oil, water or other fluid supplies lubrication, for example, to the hydraulic arms issued on a tractor or an implement attached to the tractor. The improvements relate primarily to an hydraulic tank which contains the hydraulic fluid. At present, the hydraulic systems used with tractor hitches use a tank that is attached to the hitch and is shaped more or less like a box. The problem with the present form is that when the hydraulic fluid is kept in this small box-like tank the hydraulic fluid can reach extremely high temperatures. This is due, for example, to frictional flow of the fluid or heavy or continuous use of implements. The same extremely hot hydraulic fluid makes contact with the implements and the hydraulic lift arms, and can cause the parts to break by wearing down the seals. This leads to increased cost of repair and replacement of the machinery. The extreme temperatures also make it difficult to remove or modify the positioning of the attachments in the middle of a project. Power and performance trade offs and smart hydraulic system techniques are required to prevent excessive temperatures. Thus, there is a need for a hydraulic system that will increase longevity of the machine by cooling the hydraulic fluid and preserving the seals of implements.
In order to keep the hydraulic fluid cooler the present invention provides an improved hydraulic tank that provides superior cooling of an hydraulic fluid. The design of the present invention provides increased heat dissipation that is not achieved with prior art devices. The present invention provides a larger surface area for the hydraulic tank thereby increasing the amount of heat that is dissipated and the hydraulic fluid does not become extremely hot. In prior art machines the small surface area results in hotter lubricating hydraulic fluid and thus faster wearing of parts and the faster the machine may be in need of repair.
It is generally known that the rate of convection heat transfer is observed to be proportional to the temperature difference. All material has a certain thermal resistance, the more heat energy flowing through it, the higher the temperature rise across it. Metals like copper and aluminum have very low thermal resistance, while air tends to have a relatively high resistance. A metal like aluminum with a very high thermal resistance would absorb heat produced by the hydraulic fluid and also have the advantage of quickly dissipating the heat into the air.